Active transient response circuits, system and method for digital multiphase pulse width modulated regulators

ABSTRACT

Disclosed is a multi-phase pulse width modulated voltage regulator and method in which transient voltage excursions or deviations that exceed the load line voltage by more than a predetermined amount are detected by an ATR circuit and a correction signal is applied. The correction signal is in the form of asynchronous pulses and the number of such pulses is a function of the magnitude of the voltage excursion as determined by the number of thresholds that are exceeded. Also disclosed is an adaptive voltage positioning (AVP) circuit and method for early detection of a transient event by sensing voltage changes at the load and adjusting the target voltage with pre-determined current values prior to the time that ATR event changes in the current at the load are detected. The AVP load line is pre-positioned for more precise current control. Also disclosed is an adaptive filter with adjustable frequency characteristics in response to an ATR event. Also disclosed is a pulse limiting circuit. Also disclosed is a tri-state implementation. Response to transient events is further improved with an external ATR circuit coupled to the load.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/311,115, filed on Dec. 19, 2005, now U.S. Pat. No. 7,521,913, issuedApr. 21, 2009, entitled ACTIVE TRANSIENT RESPONSE CIRCUITS, SYSTEM ANDMETHOD FOR DIGITAL MULTIPHASE PULSE WIDTH MODULATED REGULATORS, which isa continuation-in-part of U.S. patent application Ser. No. 10/938,031,filed on Sep. 10, 2004, now U.S. Pat. No. 7,570,036, issued on Aug. 4,2009, entitled MULTI-THRESHOLD MULTI-GAIN ACTIVE TRANSIENT RESPONSECIRCUIT AND METHOD FOR DIGITAL MULTIPHASE PULSE WIDTH MODULATEDREGULATORS, which claims priority from U.S. patent application Ser. No.10/103,980, filed on Mar. 22, 2002, now U.S. Pat. No. 6,965,502, issuedNov. 15, 2005, entitled SYSTEM, DEVICE AND METHOD FOR PROVIDING VOLTAGEREGULATION TO A MICROELECTRONIC DEVICE, which claims priority from theprovisional U.S. Patent Application Ser. No. 60/291,159, filed on May15, 2001, entitled METHOD AND APPARATUS FOR PROVIDING ADAPTIVE BROADBANDREGULATED POWER TO A MICROELECTRONIC DEVICE, and the provisional U.S.Patent Application Ser. No. 60/300,014, filed on Jun. 21, 2001, entitledSYSTEM AND APPARATUS FOR WIDEBAND REGULATION OF DYNAMIC LOADS USINGDISTRIBUTED TRANSIENT SUPPRESSION and claims priority from theprovisional U.S. Patent Application Ser. No. 60/638,174, filed on Dec.21, 2004, entitled ACTIVE TRANSIENT RESPONSE CIRCUITS, SYSTEM AND METHODFOR DIGITAL MULTIPHASE PULSE WIDTH MODULATED REGULATORS and incorporatesthe disclosure of such applications in their entirety by reference. Thisapplication includes subject matter that is related to and claimspriority from the foregoing applications, commonly assigned to theassignee of the present application. To the extent that the presentdisclosure conflicts with any referenced application, however, thepresent disclosure is to be given priority.

BACKGROUND OF THE INVENTION

1. Technical Field of Invention

The present invention relates, generally, to power regulation systemsand, in particular, to providing precisely regulated power to amicroelectronic device such as a microprocessor. Improved powerregulation is accomplished with an Active Transient Response (ATR)Circuit that detects multiple threshold levels and provides multiplelevels of gain. Additional improvements in power regulation areaccomplished with an External ATR Circuit, an Adaptive VoltagePositioning (AVP) Pre-positioning circuit, an Adaptive Filter, a PulseLimiting Circuit and a Tri-state implementation.

2. Background of the Invention

Regulated power supplies or voltage regulators are typically required toprovide the voltage and current supply to microelectronic devices. Theregulator is designed to deliver power from a primary source to anelectrical load at the specified current, voltage, and power efficiency.Switching power converters (SPC) also referred to as Buck regulators arecommonly used voltage regulators due to their high efficiency, highcurrent capability, and topology flexibility. In addition, they can bedesigned to provide very precise voltage and current characteristicsrequired by devices such as microprocessors, microcontrollers, memorydevices, and the like.

Power requirements for emerging leading edge technology microprocessorshave become very difficult to satisfy. As the speed and integration ofmicroprocessors increases, the demands on the power regulation systemincrease. In particular, as gate counts increase, the power regulationcurrent demand increases, the operating voltage decreases and transientevents (e.g. relatively large voltage spikes or droops at the load)typically increase in both magnitude and frequency. Some emergingmicroprocessors are expected to run on less than 1.3 volts and more than100 amperes.

SPC's utilizing step-down multi-phase Buck converters have been thepreferred topology to meet the low voltage and high current requirementsof microprocessors. With the advent of increasingly complex powerregulation topologies, digital techniques for power converter control,specifically in multiphase designs, can improve precision and reduce thesystem's total parts count while also supporting multiple applicationsin the same power system through digitally programmable feedbackcontrol.

Existing feedback controls have taken voltage measurements from theload, as well as from the individual output phases. The feedbackinformation has been used to adjust the duty cycle, i.e. width of thepulses produced by each of the phases of a multi-phase buck regulatorsystem to bring the supplied voltage and current within the load linetolerances specified by the microprocessor manufacturer. Such amulti-phase pulse width modulated (PWM) voltage regulator system hasbeen disclosed in the patent applications cross-referenced hereinaboveand the details of those disclosures are incorporated herein byreference. In particular, the co-pending patent application entitled:DIGITAL CALIBRATION WITH LOSSLESS SENSING IN A MULTIPHASE SWITCHED POWERCONVERTER, Ser. No. 10/884,840, filed Jul. 2, 2004, inventors: Southwellet al., now U.S. Pat. No. 7,262,628, issued Aug. 28, 2007, of which aninventor of this application is a co-inventor, teaches a novel losslesstechnique for sensing current at the load that is provided in a feedbackloop to bring the supplied voltage and current within the specified loadline tolerances.

Active transient response (ATR) has been used for high frequencyresponse to rapidly changing power requirement at the load by quicklyactivating multiple phases to supply or drain (as the case required)more current to or from the load, thereby temporarily overriding thegenerally slower overall voltage regulator system response. Such powerregulation systems utilizing ATR have been disclosed in detail in thepatent applications cross-referenced hereinabove and the details ofthose disclosures are incorporated herein by reference. In particular,the co-pending patent application entitled: SYSTEM, DEVICE AND METHODFOR PROVIDING VOLTAGE REGULATION TO A MICROELECTRONIC DEVICE, Ser. No.10/103,980, filed Mar. 22, 2002, inventors: Duffy et al., now U.S. Pat.No. 6,695,502, issued Nov. 15, 2005, of which an inventor of thisapplication is a co-inventor, discloses a power regulation system havingan active transient response (ATR) circuit.

The use of ATR enables voltage regulator systems to be designed withlower overall output capacitance while maintaining equivalent dynamicperformance. An ATR circuit includes a window comparator that comparesthe output supply voltage at the load to the reference voltage, asdetermined by the specified load line. As long as the output voltageremains within a specified tolerance range (i.e. window) above or belowthe specified load line, the ATR circuit provides no input signal to thePWM, which proceeds to provide power to the load in a conventionalmanner. On the other hand, as soon as the voltage is outside the“window”, the ATR circuit signals the PWM to modify its operation. Forexample, if the voltage drops below the specified voltage range, all lowside power switches in the multi-phase system are turned off and then,after a short delay, all high side power switches are turned on, causingthe normally staggered inductor charging to occur in parallel.

Thus, when the voltage at the load increases above a specified voltage,the window comparator signals an ATRL (Active Transient Response Low)event. Such an ATRL event requires a rapid lowering of the voltage atthe load. This is accomplished by turning on additional low side FETsand blocking the high side from providing the normal synchronous phasepulses. This effectively is a compensation operation that reduces theoutput voltage. Conversely, when the voltage at the load decreases abovea specified voltage, the window comparator signals an ATRH (ActiveTransient Response High) event. Such an ATRH event causes the high sideFETs to increase their duty cycle. This effectively is a compensationoperation that increases the output voltage back to within the specifiedwindow. This technique of compensating for transients causing overvoltage and under voltage conditions is enhanced by adjusting the windowcomparator to a specified load line. By using AVP (Adaptive VoltagePositioning) as a reference “target voltage”, correction of undervoltage and over voltage excursions is improved.

However, as the power regulation needs of load devices such asmicroprocessors and the like become even more demanding, even moreprecise ATR techniques than those disclosed in the aforementioned Duffyet al application, are desired. In particular, it is desired to moreprecisely detect and compensate the magnitude of the voltage excursionfrom the target voltage. In addition, it is desired to more accuratelyand quickly respond to transient power requirements of a load device.

SUMMARY OF THE INVENTION

Accordingly, the present application describes ATR techniques for moreaccurately detecting voltage excursions from the specified load line(i.e. the target voltage). In particular, the present inventiondiscloses a multi-level sensing technique that detects not only the factthat the voltage excursion requires an active transient response butalso detects the amplitude of the excursion. In accordance with theinvention, it has been found highly desirable to sense multiplethresholds, particularly multiple ATRH thresholds.

In particular, the invention provides multiple threshold based detectionof under voltage that determines how many high-side phases need to beactivated to maximize output current slew rate. For example, if thetransient is slight, only one phase will respond. If the transient issevere, up to three additional phases (e.g. in the case of a system withfour or more phases) can respond. Thus, a plurality of asynchronouspulses is provided on one or more of those phases asynchronously. Aspreviously noted, by the presently disclosed method, the number ofthresholds exceeded by the voltage excursion is detected. In short, thenumber of correction pulses provided is a function of the number ofvoltage thresholds that are exceeded. In this way, the multi-thresholdsensing scheme allows variable gain to be applied by the ATR circuit byvarying the number of ATR pulses that are generated so that thecorrection to the ATR event is in proportion to the magnitude of thesudden voltage excursion, i.e. transient.

In accordance with the invention, the multi-threshold sensing techniquecan be programmed to detect the amplitude of the excursion withindesired parameters. The detected excursion is then used to provide anadjustment to the supply voltage that is more precise than would bepossible with a less precisely detected excursion. The capability forsuch rapid enhanced response to transients allows a reduction in thebulk of output capacitors used in Buck regulators.

In accordance with another embodiment of the invention, ATR response isfurther improved by the use of an external ATR control circuit coupledto the load. ATR Comparators provide an ATRH or ATRL signal (upon theoccurrence of one of these two events) to an external ATR ControlCircuit. The external ATR Control Circuit is coupled to the load andthus provides corrective transient signals directly to the load. Theoutput of the external ATR Control Circuit is coupled to the load invarious ways such as: with a pair of external transistors connecteddirectly to the load, with a single transistor and resistive currentlimiting, or with a single transistor and inductor limiting. As afurther alternative, the external ATR Control Circuit is AC coupled tothe calibration transistor (the FET used for calibration), which thenprovides a transient correction signal to the load. The external ATRcontrol circuit provides transient current correction in addition tothat already provided by the internal ATR circuits. This is particularlyuseful, for example, when the internal ATR circuits are alreadyoperating at 100% duty cycle.

In accordance with a further embodiment of the invention, there isprovided a tri-state mode of operation in which both the high side andlow side FETs are placed in a high impedance state, i.e. OFF. A Schottkydiode is connected in parallel with the low side FET in each phase ofthe multi-phase pulse width modulated system. When both the high sideand low side FETs are in their high impedance state, the Buck convertermust draw current through the Schottky diode and the substrate bodydiode of the low side FET. This provides improved transient regulation,particularly for current going from the high state to the low state.

In accordance with a still further embodiment of the invention, ATRpulse limiting is provided. In normal operation, upon the occurrence ofan over voltage or under voltage transient event (i.e. ATRL or ATRH) theATR response is to either turn on all the low side FETs or to turn onone or more to the high side FETs to compensate to the transient eventand also to minimize overshoot and undershoot. By pulse limiting thisoverriding ATR signal (i.e. limiting the amount of time this circuit ison, then forcing it off for a fixed amount of time), the strength ofthis compensating action can be modified. This effectively changes thegain of this control mechanism. Varying gain by adjusting the on and offtimes allows the transient response of the system to be optimized.

In accordance with the invention, an Adaptive Voltage Positioning (AVP)circuit determines the voltage/current requirements to track thespecified load line, which in combination with the multi-thresholdmulti-gain ATR provides voltage regulator with enhanced performance. Inthis case, the target voltage is a variable voltage in accordance withthe specified load line. Accordingly, the target voltage used as areference for correcting for under voltage and over voltage conditions,combined with the multilevel sensing and multi-gain correction providean improved response to transient excursions. A further performanceenhancement is provided by pre-positioning the AVP specified load line.

By way of further example, in case of an over voltage condition, the ATRcircuit can activate additional low-side phases, in addition to blockinghigh-side pulses to maximize output current slew rate. As will becomemore apparent in the following more detailed description, the ATRcircuit of this invention is asynchronous relative to the synchronousPWM pulse generation. However, as a further feature, the inventionprovides a method of selecting phases when the correction pulses areapplied in accordance with a predetermined scheduled timing relative tothe synchronous pulse width modulated pulses.

In accordance with another aspect of the invention, the AVP circuitincludes a variable low pass filter that is adjusted in response to anATR event. This resolves a conflict in the choice of AVP bandwidth. Alow AVP bandwidth is desired to filter out current sense noise so thatthe AVP computation does not add a lot of noise to the output voltage.On the other hand, a high AVP bandwidth is desired for passingtransients so that the transient response looks as close to an idealvoltage step as possible. By opening up the AVP bandwidth, the amount ofovershoot associated with an ATRH event is reduced. By switching thebandwidth of an adaptive AVP filter between low bandwidth and highbandwidth modes, the regulator's voltage output ripple and transientperformance are optimized.

In accordance with a still further aspect of the invention, the AVPcircuit is configured to receive pre-determined current valuesrepresenting different threshold levels of an ATR event. Apre-positioning circuit receives these pre-determined current valuesfrom memory and provides them as an output when receiving a signalindicative of an ATRH event. The particular current value provided atthe output depends on the degree of the ATRH event, i.e. ATRH1, ATRH2,or ATRH3. These predetermined current values are added to thecompensation voltage applied to the load at a time prior to thedetection of current transients. The detection of transient currentvalues at the load is delayed because the current must pass through aninductor.

These and other features of the invention will become more apparent inthe following more detailed description and claims when considered inconnection with the drawings where like reference numerals refer tosimilar elements throughout the Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a digital multiphase buck regulatorthat was disclosed in some of the related patent applicationscross-referenced herein.

FIG. 2A is a schematic diagram of an embodiment of the inventionillustrating the connection of the ATR circuits;

FIG. 2B illustrates an exemplary AVP circuit;

FIG. 2C illustrates another embodiment of an AVP positioning circuit andadaptive AVP Bandwidth filter.

FIGS. 2D and 2E are waveform diagrams;

FIG. 2F is a schematic diagram illustrating a still further embodimentof the AVP positioning and adaptive AVP bandwidth filter;

FIG. 3 is a schematic diagram of an ATR comparator circuit in accordancewith the invention;

FIG. 4 is a circuit diagram illustrating the detection of multiplethresholds;

FIG. 5 is a waveform diagram illustrating a load line and exemplarythresholds for detecting an ATR event;

FIGS. 6A, 6B and 6C are waveform diagrams illustrating a set ofexemplary pulses generated in response to an ATR event;

FIG. 7 is a schematic diagram illustrating the multi-gain aspect of theinvention;

FIG. 8 is a series of pulse train diagrams illustrating the systemtiming for a system having four phases;

FIG. 9 is a series of pulse train diagrams illustrating the systemtiming for a system having three phases;

FIG. 10 is a series of pulse train diagrams illustrating the systemtiming for a system having six phases;

FIG. 11 is a chart illustrating the high side ATR (ATRH) schedule for asystem having multiple phases;

FIG. 12 is a schematic diagram illustrating an external ATR control withFETs;

FIG. 13 is a schematic diagram illustrating an external ATR control andFET with a resistive current limiter;

FIG. 14 is a schematic diagram illustrating an external ATR control andFET with an inductive current limiter;

FIG. 15 is a schematic diagram illustrating an external ATR control thatis AC coupled and utilizing the calibration FET to provide the externalactive transient response;

FIG. 16 is a schematic diagram illustrating a tri-state embodiment;

FIG. 17 is a schematic diagram illustrating dual input drivers to turnhigh side and low side devices on independently;

FIG. 18 is another schematic diagram illustrating dual Pulse WidthModulated Enable input drivers;

FIG. 19 is a waveform diagram illustrating the operation of thetri-state embodiment;

FIG. 20 is schematic diagram illustrating pulse limiting;

FIG. 21 is a circuit diagram illustrating a pulse limiting circuit; and

FIG. 22 is a waveform diagram illustrating the operation of the pulselimiting circuit.

DETAILED DESCRIPTION

The present invention may be described herein in terms of variousfunctional components and various processing steps. It should beappreciated that such functional components may be realized by anynumber of hardware or structural components configured to perform thespecified functions. For example, the present invention may employvarious integrated components comprised of various electrical devices,e.g. resistors, transistors, capacitors, inductors and the like, whosevalues may be suitably configured for various intended purposes. Anyactual values provided for such components as well as applied voltagelevels and currents are intended by way of example and not limitation.

In addition, the present invention may be practiced in any integratedcircuit application. Such general applications and other details thatwill be apparent to those skilled in the art in light of the presentdisclosure are not described in detail herein. Further, it should benoted that while various components may be suitably coupled or connectedto other components within exemplary circuits, such connections andcouplings can be realized by direct connection between components, or byconnection through other components and devices located therebetween.

Refer now to FIG. 1, which is a schematic diagram of a DigitalMultiphase Buck Regulator that has previously been described in detail,for example, in the cross-referenced patent applications that have beenincorporated herein by reference. It is also known as a DigitalMultiphase Buck Converter because it converts a relatively high supplypotential (+V) at e.g. 12 volts to a low voltage, e.g. 1 to 3 voltsprovided to a load at very high current levels. Digital controller 10 isshown including Digital Multi-phase Pulse Width Modulator (PWM) 20,although frequently PWM 20 is depicted as a distinct power stage. Theoutput of PWM 20 is a series of pulses on each of output lines, thephase 1 output being provided to driver 30 and the phase 2 output beingprovided to driver circuit 30′. In a multi-phase system having more than2 phases, additional phases are connected in a similar manner. Low sideFETs 50 and 52, inductors 60 and 62, and capacitor 70 are typicallydiscrete devices. In each phase, (say phase 1 for example), a pulseoutput stage comprises a high side FET (40), a low side FET (50) and aninductor (60). Similarly, the pulse output stage for phase 2 comprises ahigh side FET 42, a low side FET 52 and an inductor 62. The pulse outputstage charges up capacitor 70 and supplies power to the load. Load 80 istypically a microelectronic component, such as a microprocessor,requiring very accurate power that is regulated and maintained duringrapidly changing power requirements.

Digital controller 10 receives a VID input at voltage control 12. VID isa digital number provided by the microprocessor manufacturer describingspecific power requirements, in particular the set point, i.e. initialload line voltage at minimum current. Digital controller 10 can alsohave a reference voltage 14 that is applied to analog-digital converter16 that also receives, as a second input, the voltage at load 80. Thereference voltage from block 14 is used to calibrate the output ofanalog to digital converter ADC 16 to that reference voltage. The outputof ADC 16 is a digital voltage value that is compared to the output ofvoltage control circuit 12 (the target voltage) in summer 17 andprovided as a digital error voltage to digital compensator 18. Digitalcompensators such as digital compensator 18 that provide inputs tomulti-phase pulse width modulators, such as PWM 20 are well known anddescribed for example in the above cross-referenced patent application,SYSTEM, DEVICE AND METHOD FOR PROVIDING VOLTAGE REGULATION TO AMICROELECTRONIC DEVICE, Ser. No. 10/103,980, filed Mar. 22, 2002,inventors: Duffy et al. of which an inventor in this application is acoinventor. Digital compensator 18 then provides an input to PWM 20 inorder to modify the width of the pulses provided to the drivers 30 and30′, etc. of each of the two phases in the illustrated example, andother phases, when utilized. Phase 1 is driven by driver circuits 32 and34. Circuit 32 drives the gate of FET 40 with a signal that iscomplementary to the output of circuit 34 that drives the gate of FET50. FET 40 and 50 have their drain-source paths connected in series, ata common point A, between a first potential source (+V) and a secondpotential source (ground). Since both FET 40 and 50 are shown asN-channel devices, only one of the two transistors is on at any onetime. Of course, if transistor 40 were to be replaced with a P-typetransistor, then the same phase signal could be used to drive the gateof both transistor 40 and 50. In either case, there is never a directcurrent path between +V and ground.

The phase 2 output of PWM 20 is provided to circuits 36 and 38 duringphase 2 time in the same way that circuits 32 and 34 receive the pulsewidth modulate signals during phase 1 time. Circuit 36 then drives thegate of FET 42 and circuit 38 drives the gate of FET 52. Note thatalthough two phases are shown, any number of phases can be used. Largernumber of phases provides smoother and more accurate power to the load.

In operation, during phase 1, while the pulse width modulated waveformturns high side FET 40 on, current flows through FET 40 into node A andthrough inductor 60 to charge capacitor 70 and provide power to load 80.On the other hand, when low side FET 50 is turned on, current flowsthrough FET 50. High side FET 42 and low side FET 52, connected incommon at node B operate in a similar manner during phase 2. The voltagefrom the load 80 is fed back to ADC 16 so that the voltage to the loadcan be adjusted to changing load conditions. It is desirable to alsomeasure the voltage at node A and node B (and other corresponding nodesin systems with more phases) as an indication of the current beingsupplied to the load. The cross-referenced patent applications show howthe measurements taken at nodes A and B are then used to better regulatethe power provided to load 80. Although such a system operatessatisfactorily, it has been found that for more rapid response to highspeed variations in the power requirements of load 80, a second voltageadjustment technique is desired. In particular, when the voltageexcursion from the load line exceeds a predetermined specified amount,then a secondary power adjustment is provided by active transientresponse (ATR) circuitry.

Refer now to FIG. 2A, which is a schematic diagram of one embodiment ofthis invention. Components corresponding to FIG. 1 have been identifiedwith corresponding reference numerals. Multi-phase pulse width modulator20 is coupled to the pulse output stage of each phase through drivers 30and 30′. As in FIG. 1, each pulse output stage comprises a high side FET(40, 42), a low side FET (50, 52) and an inductor (60, 62), as a twophase system is shown. Additional phases would comprise similarstructure.

In the FIG. 2A embodiment, voltage control is provided by AdaptiveVoltage Positioning block AVP12. As in FIG. 1, AVP12 gets a VID input.As shown in FIG. 2A, AVP12 also gets an RLOADLINE input, which is anumber provided by microprocessor manufacturers indicating the desiredslope of the load line. AVP 12 receives an additional input from currentADC13. Current from all the phases at the nodes (node A and node B inthe illustrated two phase example) is sensed through resistor R15 andresistor R15′, clocked through multiplex circuit 11 at the active phasetime and converted to a digital value in ADC 13. This permits AVP12 toprovide an adjustment to the target voltage number provided tocomparator 17 and active transient response circuit ATR circuit 100.Thus, the target voltage is determined by AVP circuit 12 which adjuststhe target voltage in accordance with the specified load line. Inaddition, AVP12 receives inputs from ATR circuit 100 for providing earlyand predictive correction of the target voltage, as will be described ingreater detail hereinbelow.

ATR circuit 100 is coupled between the output stage, at load 80 andmulti-phase PWM20 and is configured to detect the voltage level at theload. In case the transient voltage at the load deviates from the targetvoltage by one or more of the pre-set thresholds, ATR100 provides asignal to PWM20 that is a function of the amplitude of the deviation ofthe detected voltage from the target voltage. The ATR100 output will beone of: ATRL, ATRH1, ATRH2, or ATRH3.

ATR100 is also coupled between the output stage, at load 80, and AVP12to provide one of the signals indicative of an ATR event, i.e. one ofATR signals (ATRL, ATRH1, ATRH2, or ATRH3) to AVP12. This enables AVP12to provide an early, predictive change to summer17. This predictivechange can occur prior to the time that the sensed current change isreceived from ADC13 because the sensed load current change is delayedpassing through inductors 60, 62, and other similar inductors inadditional phases.

As long as the voltage at the load is maintained within predeterminedlimits, ATR circuit 100 is not activated and no output signals areprovided by ATR circuit 100. However, when the changes in power demandsby the load result in a voltage excursion at the load that exceeds thepredetermined limits, ATR circuit 100 provides ATRL, ATRH1, ATRH2, orATRH3 signals to PWM generator 20 to correct the voltage deviationrapidly and with minimal noise generation. As shown in FIG. 2A, thesesame signals are provided to AVP12.

Refer now to FIG. 2B illustrating one embodiment of ADP12. The sensedcurrent from ADC 13 is received at demultiplexer circuit (demux) 202.Demux 202 also receives a phase clock corresponding to the time of eachphase output of PWM 20. In this case, a six phase example is illustratedso that there are in fact 6 phase clock inputs. Demux 202 provides eachof the channel currents ICH1, ICH2, ICH3, ICH4, ICH5, and ICH6 to summercircuit 204, which in turn provides the sum of the currents (ISUM) onall of the channels to multiplier circuit 206. ISUM is thus the rotatingsum of the currents of all phases. The output of summing circuit 204 isprovided to multiplier circuit 206, where it is multiplied by RLOADLINE,which is a constant number representing the specified slope of the loadline. The output of multiplier 206 is therefore a voltage valuerepresenting the change in voltage (VDELTA_AVP) resulting from thechanging total current ISUM. This value is passed through a low passdigital fitter in order to pass as little ripple noise as possible. Thefiltered output voltage (FILT VDELTA AVP) is provided to summing circuit210, which also receives the VID input. Vout, the output of summingcircuit 210 is then the VID set point value as modified by the sensedcurrent. Although an AVP12 in accordance with this embodiment operatessatisfactorily, it has also been found that Vout is delayed undesirably.This is due to the fact that the sensed current input to DEMUX 202 isdelayed in time because current at load 80 is sensed through N inductors60, 62, etc. (N being the number of phases in a system.) The eliminationof this delay and other improvements are provided by the circuit of FIG.2C.

Refer now to FIG. 2C in which elements corresponding to FIG. 2B havebeen similarly numbered and function in the same manner. Theaforementioned elimination of delay is provided at summing circuit 205,which receives a pre-positioning signal (CUR_INJECT) which is added toISUM to produce ISUM+CUR_INJECT. This larger current value is multipliedby the RLOADLINE (load line slope constant) to produce a larger DELTAAVP. This larger changed voltage value is provided to digital low passfilter 208′, which is also improved from the FIG. 2B embodiment.

In particular, for normal signals, it is desired that a digital filter,such as 208′, have a narrow bandwidth with filter coefficients set atFC1, for example to filter out ripple noise so that the AVP computationdoesn't add a lot of noise to the output voltage. However, for highfrequency transient signals a wide bandwidth filter with filtercoefficients set at FC2, for example, is desired so that transientresponse looks as close to an ideal voltage step as possible. Thesecoefficients are set by 2:1 multiplex circuit 212, as will now bedescribed.

Circuit 212 receives a (FILTER_WIDE_BW) input when there is either anATRL or an ATRH event. The second input (FILTER_NARROW_BW) is activewhen there is no ATR event. OR circuit 214 is also provided to providean input to circuit 212 when either an ATRL1 or an ATRH1 event occurs.Circuit 212 will pass the FILTER_WIDE_BW signal when S=1, i.e. eitherATRL1 or ATRH1 is up. Conversely circuit 212 will pass FILTER_NARROW_BWwhen S=0. Depending on which of these signals is inputted to digitalfilter 208′, it will operate with coefficient FC1 or FC2.

Pre-positioning circuit 216 receives pre-stored inputs (from memory notshown) representing current values corresponding to ATRH thresholdsexceeded. For example, CUR_INJECT_ATRH1 could be preset at 25 Amps.Then, CUR_INJECT_ATRH2 could be preset at 50 amps. CUR_INJECT_ATRH3could be preset at 75 amps and so on for the N thresholds. Logic circuit218 receives the inputs ATRH1, ATRH2 and ATRH3 from ATR circuit 100.Note that ATR circuit 100 receives a voltage sense input directly fromthe load 80. This voltage transient signal is received much more quicklythan the current sense signal transient which must pass through aninductor, e.g. 60, 62, etc. In response to a voltage transient, ATRcircuit 100 inputs to logic circuit 218, the ATRH threshold (if any)that has been triggered. In response, circuit 216 provides thepre-programmed values of CUR_INJECT to summing circuit 205. For example,the respective pre-programmed values of CUR_INJECT can be: O amps (noATR), 25 amps (ATRH1 event), 50 amps (ATRH2 event) or 75 amps (ATRH3event). In turn, summer 205 provides the sum of the currentsISUM+CUR_INJECT to multiplier 206. The output of circuit 206 is avoltage (DELTA_AVP) that is the product of RLOADLINE (the slope of theload line) and the current. It is the function of AVP Low pass filter208′ to filter this voltage. Filter 208′ receives a signal from circuit212 and depending on that signal acts as a low pass filter either withcoefficient FC1 or FC2 to provide the filtered output to summer 210.Summer 210 combined the VID_SET_POINT value with the filtered voltagevalue as the output of the AVP12 circuit.

FIG. 2D illustrates the improved waveform provided by using variabledigital filter 208′. Waveform A is provided by using digital filter 208′while waveform B shows the waveform that is provided when digital filter208′ is not tuned to the correct bandwidth. The significant differencein the two waveforms is illustrated by the arrow. The values of 0 Ampsand 100 Amps are shown by way of example. With further reference to thewaveform in FIG. 2D, note that it has a delay “C”. This delay has beeneliminated in waveform A′ in FIG. 2E, which essentially is the samewaveform A shown in FIG. 2D, but without the delay. As previouslydescribed, the delay is eliminated with pre-positioning circuit 216.

Refer now to FIG. 2F, which is a schematic diagram illustrating a stillfurther embodiment of the AVP positioning and adaptive AVP Bandwidthfilter. Refer also to FIG. 2C and note that corresponding elements havebeen identified with the same reference numerals and function in thesame manner. The previously described elimination of delay is providedat summing circuit 205, which receives a pre-positioning signal(CUR_INJECT) from latch 216 and a signal from latch 220 which are addedto ISUM in summer 205. This larger current value is multiplied by theRSLOPE (PREVIOUSLY IDENTIFIED AS RLOADLINE, i.e. load line slopeconstant) to produce a larger DELTA AVP. This larger changed voltagevalue is provided to digital low pass filter 208′.

In particular, for normal signals, it is desired that a digital filter,such as 208′, have a narrow bandwidth with filter coefficients set atFC1, for example to filter out ripple noise so that the AVP computationdoesn't add a lot of noise to the output voltage. However, for highfrequency transient signals a wide bandwidth filter with filtercoefficients set at FC2, for example, is desired so that transientresponse looks as close to an ideal voltage step as possible. Thesecoefficients are set by 2:1 multiplex circuit 212 (see FIG. 2C), whichprovides the ATRL and ATRH inputs to Filter 208′. Upon the occurrence ofeither ATR event (ATRL or ATRH), digital filter 208′ will operate withfilter coefficients set at FC2. It is the function of AVP filter 208′ tofilter the voltage received from multiplier 206 and to provide thefiltered output to summer 210. Summer 210 combines the VID_SET_POINTvalue with the filtered voltage value as the output of the AVP12circuit.

Refer now to FIG. 3 for a more detailed description of the comparatorcircuit 300 used in the ATR circuit 100. The comparator comprises 4programmable threshold setting circuits 302, 304, 306, and 308.Threshold detector 302: 1. Receives as an input, the analog value of thetarget voltage VADP from AVP12, 2. Adjusts that input by an amount thatis the ATRL threshold e.g. 50 mv and 3. Provides that value tocomparator circuit 310. Comparator circuit 310 also receives, as asecond input, the actual voltage sensed at the load. Since the VADPreference signal is in digital form, it is converted to an analog valuein DAC312. Thus, whenever the voltage sensed at the load has anexcursion that exceeds the ATRL threshold, comparator circuit 310provides an output that indicates that there is an ATRL event.Comparator circuit 310 is configured to receive the aforementioned inputsignals in analog form and to provide the output in digital form. Thoseskilled in the art will know of various topologies for comparing twoanalog signals and providing a digital output (e.g. with an analog todigital converter integrated with the compare circuit. The ATRL pulseblocks the high side FETs and turns on the low side FETs as the outputof the pulse width modulator 20 provides complementary outputs.

The ATRH comparator circuits 314, 316, and 318 are configured in thesame way and operate in a manner similar to comparator circuit 310.Threshold setting circuit 304 sets the threshold voltage level ATRH1 forcomparator 314. When the Vsense voltage deviates (in a negativedirection in case of an ATRH event) to a greater value than thethreshold voltage provided by block 304, comparator 314 provides a highlevel logic signal indicating an ATRH1 event. If the Vsense voltagedeviates to a greater value than the threshold value provided by block306, comparator 316 provides a signal indicating an ATRH2 event. If theVsense voltage deviates to a greater value than the threshold valueprovided by block 308, comparator 318 provides a signal indicating anATRH3 event.

Refer now to FIG. 4, for a description of the multi-threshold ATRcomparator circuit 400. The output voltage Vsense is received from theload at the gate of FET402. The analog value of VADP, i.e. Vtarget, isreceived at the gate of FET404, as converted into analog form byDAC312′. DAC406 receives the pre-determined ATRL threshold level indigital form and provides an analog current to a voltage dividercomprising Resistors R1, R2, R3, and R4. The voltage at the commonconnection of R3 and R4 then sets the ATRL threshold at comparator 410.DAC408 provides a current to a voltage divider comprising Resistors R5,R6, R7, and R8. DAC 406 and DAC 408 are differential current DACs thatset the threshold for the ATR comparator circuits by generating anoffset voltage across resistors R1-R4 and R5-R8, respectively.

The inputs Thresh_ATRL and Thresh_ATRH are programmable parametersstored in memory, which set the current DAC outputs. These programmableparameters are digital values permitting adjustment of ATRH1, ATRH2, andATRH3 by simply modifying the value of the Thresh_ATRH input to currentDAC 408. Similarly, the ATRL threshold is programmable by simplyadjusting the value of the Thresh_ATRL, input to current DAC 406.Differential current outputs are used so that the current through FETs402 and 404 are fixed independent of setting (i.e. the sum of the trueand complement currents are a fixed value).

In operation, the voltage at the common connection of R3 and R4 isapplied as a first input to ATRL compare circuit 410. This voltage valueis determined by: 1. the amplitude of the target voltage applied to thegate of FET404, 2. the amplitude of the current supplied by DAC406 and3. the value of the resistors in the voltage divider formed by R1, R2,R3, and R4. The voltage at the common connection of R8 and FET402 isapplied to the second input to ATRL compare circuit 410. The voltage atthis second input is determined by the amplitude of the sensed voltageapplied at the gate of FET402. If the second input exceeds the firstinput, compare circuit 410 will signal an ATRL event (ATRL1) resultingin the blocking of high side FETs and turning on low side FETs.

Comparator circuits 412, 414, and 416 are configured and operate in amanner similar to just described circuit 410. Each of them receives afirst input that is a function of the target voltage applied to the gateof FET 404. Each of them receives a second input that is a function ofthe sensed voltage provided to the gate of FET 402, the thresholdsetting current provided by current DAC 408 and the resistor values ofR5, R6, R7, and R8. In particular, comparator circuit 412 receives thesensed input from the common connection between R7 and R8. In the eventthe voltage sensed at the common connection between R7 and R8 deviatesfrom the target voltage by a value greater than the first threshold,then circuit 412 provides an output indicating an ATRH1 event. If thevoltage at the common connection of R6 and R7 deviates from the targetvoltage by a value greater than the second threshold, as set incomparator circuit 414, then circuit 414 provides an output indicatingan ATRH2 event. Lastly, if the voltage at the common connection of R5and R6 deviates from the target voltage by a value greater than thethird threshold, as set in comparator circuit 416, then circuit 416provides an output indicating an ATRH3 event.

Thus, setting a single threshold at a voltage level in a positivedirection (at a pre-determined voltage higher than the target voltage)permits detection of a deviation greater than the pre-determinedvoltage. The detection of such a deviation signals an ATRL eventactivating circuitry to rapidly reduce voltage at the load. On the otherhand, setting multiple thresholds at voltage levels in a negativedirection (at multiple voltage levels lower than the target voltage)permits detection of the size of the deviation from the target voltage.The detection of such multiple levels of deviation, i.e. transients,signals not only the existence of an ATRH event, but also the amplitudeof the deviation, i.e. ATRH1, ATRH2, or ATRH3.

The operation of the ATR comparators and ATR circuit 400 will also beunderstood with reference to the waveform shown in FIG. 5. FIG. 5 showsan AVP load line well known in the art. The amplitudes of Load voltage(V), Load current (A) and the slope of the AVP Load line are specifiedby the manufacturer of the load. Most typically, loads requiringprecisely controlled low voltage levels at high currents under rapidlychanging load conditions are microprocessors, microcontrollers, and thelike. The specified error limits shown are also provided by themanufacturer of the load. Under normal operating conditions, the voltageand current provided to the load are expected to stay within thespecified error limits, for example +/−19 millivolts.

Under rapidly changing conditions, for example if the load suddenlyrequires far less current, the load at the voltage could exceed the AVPload line voltage by more than the pre-set ATRL threshold. This is anATRL event that will cause the ATR circuit 100 to be activated torapidly bring the load voltage towards the AVP load line. Similarly, ifthe load suddenly requires far more current, then the load voltage coulddecrease to an amount that would exceed one or more of the ATRHthresholds. This will be an ATRH event that will cause the ATR circuit100 to be activated to rapidly bring the load voltage towards the AVPload line.

In accordance with the invention, it has been found highly desirable tohave multiple thresholds, particularly multiple ATRH thresholds. All ofthe embodiments in this application disclose three ATRH thresholds, towith, ATRH1, ATRH2 and ATRH3, which can be used to great advantage inPWM systems with 2-6 or more channels (phases). However, there is nopractical reason why rather than 3 ATRH thresholds, 2, 4 or more ATRHthresholds could not be used. However, the use of multiple ATRHthresholds greatly improves circuit operation (as compared with a singleATRH threshold) and is more cost effective than 4 or more ATRHthresholds where the improved performance may reach the point ofdiminishing returns. The improvement in circuit operation is achieved byadjusting the magnitude of the ATR response to the magnitude of theexcursion from the AVP load line.

The advantage of detecting multiple ATR thresholds is achieved byproviding correction based on the magnitude of the excursion. Thistechnique is shown in the waveform diagram of FIG. 6A; which showsexemplary timing pulses in a four phase system. The Vout waveformillustrates (in dotted lines) the likely output waveform when ATR is notused. A sudden high current demand causes the voltage to dropsubstantially and then gradually return to a lower steady state than theprior steady state level in accordance with the AVP load line. Themethod disclosed herein provides a pulse width modulator configured toprovide multi-phase pulse outputs. In the FIG. 6A case, there are fourchannels (phases), to with PWM1, PWM2, PWM3, and PWM4, each providing anoutput pulse during its assigned time slot, as shown. In accordance withthe method, each of the illustrated pulses has a width (duty cycle) thatcan be narrower or wider to maintain the desired regulated voltageduring normal operation.

With continued reference to FIG. 6A, and in particular to the areaidentified as an ATR Transient Event, note the Asynchronous PWMActivity. In this method step, a plurality of asynchronous pulses areprovided on one or more of those phases that are not already providing a“normal” synchronous pulse width modulated pulse output. As previouslynoted, by the presently disclosed method, the number of thresholdsexceeded by the voltage excursion is detected. The number of correctionpulses provided is a function of the number of voltage thresholds thatare exceeded. Refer to line PWM1 which shows the occurrence of the firstATR pulse occurring shortly after the Vout voltage dropped. Asillustrated, this first ATR pulse occurs at a point in time when the“normal” synchronous phase pulse PWM2 is already off and PWM3 is justturning on. This first pulse occurs in response to an ATRH1 event sothat at this point only the first threshold has been exceeded. In somecases, it is possible that at this point the voltage excursion isreturned to normal and no more ATR pulses are required. However, in theFIG. 8 illustration, additional ATR pulses are provided. As illustrated,a total of 4 ATR pulses occur on PWM1, 3 on PWM2, 1 on PWM3 and 1 on PWM4. The last of the ATR pulses occur while “normal” synchronous PWM 4 isalso on. As a result of the ATR pulses, the Vout voltage (solid line)dropped less than it would have without ATR. The multi-threshold sensingscheme allowed variable gain to be applied by the ATR circuit by varyingthe number of ATR pulses that are applied so that the correction to theATR event is in proportion to the magnitude of the sudden voltageexcursion, i.e. transient.

By way of further example, see FIG. 6B illustrating a two-phase systemas in FIG. 2A. As previously noted, additional phases, when used,operate in a similar manner. Vout is the voltage at the load. Upon theoccurrence of an ATRH event (a down transient sufficient to trigger oneor more ATRH threshold levels), the extra PWM pulses (in the circledarea) are found at node A (V_(A)) and node B(V_(B)). Refer now to FIG.6C; which illustrates how in the case of an ATRL event, the waveformsshown in FIG. C occur at Vout and nodes A and B. An up level transientthat exceeds the ATRL threshold causes the ATRL event. Such an up leveltransient is caused when the current demand of the load decreases. Inthis case, PWM pulses are blocked at nodes A and B, by for example lineATRL1 in FIG. 7. This permits Vout to be brought down quickly from itsup level spike. In each case (FIG. 6B and FIG. 6C), the new voltagelevel at Vout is set in accordance with the new current demands of theload causing the new voltage to be positioned in accordance with theload line (see FIG. 5) in accordance with known AVP techniques.

The multi-gain aspect is illustrated in greater detail in the schematicdiagram of FIG. 7. For purposes of illustration, only one phase isshown. A multi-phase system will have one such FIG. 7 circuit for everyphase. However, it will be appreciated by those skilled in the art thata feature of this invention is accomplished with the capability ofproviding ATR compensation pulses on one or more phases, in addition tothe normal synchronous pulse width modulated phase pulses. PWM 700receives a clocking signal and a phase signal (labeled phase x) for theparticular phase with which it is associated. (In the four phase systemillustrated in FIG. 8, these are the phase 1, phase 4, phase 2 and phase3 signals.) It also receives a duty cycle signal from digitalcompensator 18 (FIG. 2A) to adjust the pulse width. The output is aninternal pulse width modulated pulse train pwm_internal that is inputtedto OR logic circuit 702, which in turn provides this signal to AND logiccircuit 704. This pulse width modulated pulse train becomes the outputof the multi-phase PWM generator, e.g. PWM 20 (FIG. 1). However, thispulse train output is blocked by AND logic circuit 704 when an input isreceived as an ATRL event, for example from ATRL1 (FIG. 3 or 4). In caseof an ATRL event, the output voltage has exceeded the ATRL threshold(FIG. 5) and pulses are applied only through low side FETs to bring theoutput voltage down. In case the output voltage drops sufficiently belowthe AVP load line to exceed one or more of the ATRH thresholds (ATRHevent), then a high level logic input is received at the correspondingAND logic circuit 706, 708, and 710. AND circuit 706 also receives adocking signal ATRH1_PHASEX (from timing generator 701) in order to gatethe ATRH1 signal through AND logic gate 706 at the appropriate time, aswill be explained in connection with a timing diagram (FIG. 8). ANDlogic gate 706 passes this signal to OR logic gate 712, which in turnpasses the signal through OR logic gate 702 to AND logic gate 704. Sincean ATRH event will not occur simultaneously with an ATRL event, theATRH1 signal will become the output pwm_out. The ATRH2 signal is clockedthrough AND logic gate 708 and the ATRH3 signal is clocked through ANDlogic gate 710 and eventually to the output pwm_out in the same way asATRH1 at the occurrence of the corresponding PHASEX signal from timinggenerator 701.

Refer now to FIG. 8, which illustrates the timing of pulse signals in afour phase system. As illustrated, phase 1, phase 4, phase 2 and phase 3signals are generated to operate a four phase system. In the PWM1waveform, the pulses that are labeled as ATRL1 are the “normal”synchronous pulses that occur during phase 1 time, unless of courseblocked by an ATRL event, in which case the low side FETs are turned on.The operation of PWM4, PWM2 and PWM3 is similar. ATRL1 labeled pulsesare provided by PWM4 during phase 4 time. Similarly, PWM2 provides“normal” synchronous pulses during phase 2 time and PWM3 provides“normal” synchronous pulses during phase 3 time. The labeled pulses forthe PWM1, PWM4, PWM2 and PWM3 occur as an ATRH output at the indicatedtime as gated by the timing pulses shown in the remainder of the FIG. 8waveform diagram.

The pulse trains with the illustrated timing of the ATRHX_PHASEX signalsare generated by timing generator 701 in response to the CLK inputpulse. Thus, as shown in FIG. 8, the atrh1_phase1 clock signal gates theatrh1 signal to occur on PWM1 at the designated times, in case the atrh1threshold was exceeded. Similarly the atrh1_phase4 pulse gates the atrh1signal to PWM4. The atrh1-phase 2 pulse gates the atrh1 signal to PWM2and the atrh1_phase3 pulse gates the atrh1 signal to PWM3. In case theATRH2 and ATRH3 thresholds are exceeded, these signals are similarlygated at the indicated times to the indicated channel of the pulse widthmodulator.

As previously noted, the three ATRH threshold level detection is usefulnot only in four phase systems but in a system with any number ofphases. For example, see FIG. 9 which illustrates timing for a systemhaving three phases. The various pulse trains: phase 1, phase 2, phase4, PWM1, PWM2, and PWM3 are generated as in the prior example; howeverwith only 3 phases, as shown. With a 3 phase system, ATRH1 is activatedwhen the first threshold is triggered and ATRH2 is activated when thesecond threshold is triggered. However, if and when the third thresholdis triggered, the ATR circuit has no effect in a three phase system.Similarly, in a two phase system, in case of an ATRH event, only ATRH1correction pulses are provided.

By way of example, see FIG. 10, where the system timing for a six phasesystem is shown. The various pulse trains: phase 1, phase 2, phase 4,phase 5, phase 6, PWM1, PWM2, PWM3, PWM4, PWM5 and PWM6 are generated asin the prior example; however with the 6 phases, as shown. Thus,whenever more than 4 phases are provided with three threshold detectors,in case of an ATRH event that triggers all three thresholds, all ATRHpulses (atrh1, atrh2 and atrh3) are used. The ATRL events, beingtriggered by one threshold, remain the same regardless of the number ofphases. In all cases, the ATRL and ATRH are mutually exclusive andcannot occur simultaneously. Also, as previously noted, in case of anATRL event, the “normal” synchronous phase pulse is blocked, as well. Byway of further detailed explanation see FIG. 11 showing a schedule ofphase selection for any number of phases from 2 to 6. Thus, although thecorrection pulses provided in response to an ATRH event areasynchronously generated in different phases, the phases are selected inaccordance with a predetermined scheduled timing relative to the normalsynchronous pulse width modulated pulses.

Refer now to FIG. 12, which is a schematic diagram of another embodimentof this invention. Components corresponding to FIG. 2A have beenidentified with corresponding reference numerals. Multi-phase pulsewidth modulator 20 is coupled to the pulse output stage of each phasethrough drivers 30 and 30′. As in FIG. 2A, each pulse output stagecomprises a high side FET (40, 42), a low side FET (50, 52) and aninductor (60, 62), as a two phase system is shown. Additional phaseswould comprise similar structure.

In the FIG. 12 embodiment, voltage control is provided by AdaptiveVoltage Positioning block AVP12. As in FIG. 1, AVP12 gets a VID input.As shown in FIG. 2A, AVP12 also gets an RLOADLINE input, which is anumber provided by microprocessor manufacturers indicating the desiredslope of the load line. AVP 12 receives an additional input from currentADC13. Current from one phase only is sensed at node B in theillustrated two phase example) is sensed through resistor R15 andconverted to a digital value in ADC 13. This permits AVP12 to provide anadjustment to the target voltage number provided on line 12′ to summer17 and active transient response comparators ATR comparators 100. Thus,the target voltage is determined by AVP circuit 12 which adjusts thetarget voltage in accordance with the specified load line. In addition,AVP12 receives ATRL and ATRH inputs from ATR comparators 100 forproviding early and predictive correction of the target voltage, as willbe described in greater detail hereinbelow.

ATR comparators 100 are coupled between the output stage, at load 80 andmulti-phase PWM20 and are configured to detect the voltage level at theload. In case the transient voltage at the load deviates from the targetvoltage by one or more of the pre-set thresholds, ATR100 provides asignal to PWM20 that is a function of the amplitude of the deviation ofthe detected voltage from the target voltage. The ATR100 output will beATRL or ATRH. ATRH can be any one of: ATRH1, ATRH2, or ATRH3 but wouldusually be ATRH1.

ATR100 is also coupled between the output stage, at load 80, and AVP12to provide one of the signals indicative of an ATR event, i.e. one ofATR signals (ATRL or ATRH) to AVP12. This enables AVP12 to provide anearly, predictive change to summer 17. This predictive change can occurprior to the time that the sensed current change is received from ADC13because the sensed load current change is delayed passing throughinductors 60, 62, and other similar inductors in additional phases.

As long as the voltage at the load is maintained within predeterminedlimits, ATR comparator 100 is not activated and no output signals areprovided by ATR 100. However, when the changes in power demands by theload result in a voltage excursion at the load that exceeds thepredetermined limits, ATR 100 provides ATRL or ATRH, signals to PWMgenerator 20 to correct the voltage deviation rapidly and with minimalnoise generation. As shown in FIG. 2A, these same signals are providedto AVP12.

With continued reference to FIG. 12, note series connected high side FET40′ and low side FET 52′ directly coupled to the output of the regulatorand load 80. The gates of FET 40′ and 52′ are coupled to the outputs ofExternal ATR Control 101. External ATR Control 101 has its inputscoupled to the outputs of ATR Comparators 100. In operation, externalATR Control operates only if it receives an ATRL or ATRH input. In caseof an ATRL input signal, FET 52′ is turned on. In case of an ATRH inputsignal, FET 40′ is turned on. This provides an additional current paththrough the conducting one of these two FETs (40′ or 52′) to rapidlycompensate for the transient event. By way of example, if the maximumduty cycles of high side FET 40 provide 65% of additional currentrequired to compensate for the transient event, then FET 40′ providesthe additional 35% for a desired 100% transient compensation.

Refer now to FIG. 13, which is a schematic diagram of another embodimentof this invention. Components corresponding to FIG. 12 have beenidentified with corresponding reference numerals. Multi-phase pulsewidth modulator 20 is coupled to the pulse output stage of each phasethrough drivers 30 and 30′. As in FIG. 12, each pulse output stagecomprises a high side FET (40, 42), a low side FET (50, 52) and aninductor (60, 62), as a two phase system is shown. Additional phaseswould comprise similar structure. The difference to be noted in FIG. 13is the addition of current limiting resistor R16 and the absence of highside FET 40′. In this embodiment, External ATR Control 101 provides aninput to FET 52′ in the event of an ATRL event to conduct transientcompensating current between the load and ground potential. This extracurrent conduction path is significant for compensating for an ATRLtransient.

Refer now to FIG. 14, which is a schematic diagram of another embodimentof this invention. Components corresponding to FIG. 13 have beenidentified with corresponding reference numerals. Multi-phase pulsewidth modulator 20 is coupled to the pulse output stage of each phasethrough drivers 30 and 30′. As in FIG. 13, each pulse output stagecomprises a high side FET (40, 42), a low side FET (50, 52) and aninductor (60, 62), as a two phase system is shown. Additional phaseswould comprise similar structure. The difference to be noted in FIG. 14is that inductor 64 limits the current through FET 52′ instead ofresistor R16 that performed the current limiting function in FIG. 13.

Refer now to FIG. 15 which is a schematic diagram of another embodimentof this invention. Components corresponding to FIG. 13 have beenidentified with corresponding reference numerals. Multi-phase pulsewidth modulator 20 is coupled to the pulse output stage of each phasethrough drivers 30 and 30′. As in FIG. 13, each pulse output stagecomprises a high side FET (40, 42), a low side FET (50, 52) and aninductor (60, 62), as a two phase system is shown. Additional phaseswould comprise similar structure.

In the FIG. 15 embodiment, External ATR Control 101 is AC coupled toexternal low side FET 52′ through capacitor 71. This AC coupling limitsthe time that an up level signal will keep FET 52′ on. This is not aproblem as the short duration of transients (and the corresponding shortduration of correction signals) is within the time frame that FET 52′needs to be on. In the FIG. 15 embodiment, Calibration Current Control102 is coupled to FET 52′ through resistor R17. The previously describedcalibration function is performed during initialization when FET 52′ isreferred to as a calibration FET with calibration resistor R16. Duringnormal circuit operation, Calibration Current Control 102 remains off.As thus illustrated, in the FIG. 15 embodiment FET 52′ (as well asresistor R16) are “shared” and perform the function of calibration orthe function of compensating for transients. This sharing of componentsis cost effective.

Refer now to FIG. 16 illustrating driver circuits that provide atri-state mode of operation in which both the high side FET and the lowside FET are turned off. As in drawing figures in previous embodiments(see e.g. FIG. 15), a two phase system is illustrated. A first phase hashigh side FET 40 and low side FET 50 series connected between +V andground potential with the common node A therebetween connected toInductor 60. Inductor 60 is coupled to capacitor 70 and load 80.Similarly, the second phase has high side FET 42 and low side FET 52series connected between +V and ground potential with the common node Btherebetween connected to Inductor 62. Inductor 62 is also coupled tocapacitor 70 and load 80. An alternative way to implement this Buckconverter circuit function is to replace the low side FETs (in this case50 and 52) with diodes. Depending on the application, a diode may bepreferred in place of a low side FET.

In a Buck converter having a high side FET and a low side FET, the dutycycle of the high side FET is increased when a higher current isdemanded by the load and the duty cycle of the low side FET is increasedwhen a lower current is demanded by the load. When switching betweenturning on the high side or low side FET, there is a brief interval whenboth FETs are off to avoid creating a DC current path from +V to groundpotential. However, in Buck converters utilizing a diode in place of thelow side FET, the diode begins to conduct immediately when the commonnode (e.g. A or B) drops one diode threshold below ground potential. Byway of further explanation, FETs inherently have substrate diodes (alsoknown as body diodes) that are usually not shown. Thus, FET 50 has bodydiode 51 and FET 52 has body diode 53. These body diodes conduct currentwhenever the voltage drop from ground to the common node exceeds thethreshold level of the diode. (Obviously, FETs 40 and 42 also have bodydiodes but these are not relevant to the present explanation.)

With continued reference to FIG. 16, note Schottky diode 54 connected inparallel to FET 50 between node A and ground potential and Schottkydiode 56 connected in parallel to FET 52 between node B and groundpotential. These also conduct as soon as their threshold levels areexceeded and avoid the creation of extremely high negative voltages thatcan occur at the common nodes A and B. In order to quickly compensatefor transients at the load, it is desirable to maximize the outputcurrent slew rate. (Slew rate is defined by how quickly current canchange through the inductor, e.g. 60 and 62.) Slew rate (di/dt) is equalto V/L where V is the voltage across the inductor having inductance L.Assuming an output voltage (Vout) of approximately 2 volts, the voltagedifference through the high side FET connected to +V (c. 12 volts) isfar greater than the voltage difference through the low side FETconnected to ground potential. It has been found that by placing boththe high side FET and low side FET (e.g. 40 and 50) in a high impedancestate when the current through the inductor is positive (i.e. beingsourced from the power stage to the load), the current will flow throughthe Schottky diode or body diode, and the voltage across the inductorwill be the output voltage plus the forward voltage of the diode, whichmaximizes the rate at which the current through the inductor is reducedcompared to simply turning on the low side FET.

In order to achieve a tri-state output at nodes A and B (by putting boththe high side and low side FET in a high impedance state), the input toeach gate electrode must be held below threshold level. In the FIG. 16embodiment, tristate control in one phase is obtained with the use ofseries connected resistors R16 and R17 having their common connectionconnected to the inputs of driver circuit 32 and 34. Driver circuit 32provides an output when the input exceeds its threshold Vth. Drivercircuit 34 provides an output when the input drops below Vtl. In theabsence of an input from controller 1600 on the PWM line, the voltage atthe node connecting R16 and R17 will reach a mid-point between +V andground and the resultant output of drivers 32 and 34 will keep both FET40 and 50 off. Of course, when the controller receives an internalenable signal then the internal pulse modulated signal PWM is outputtedto the drivers and the respective high and low side FETs.

With continued reference to FIG. 16, note that in the second phase,tristate control is obtained with the use of series connected resistorsR18 and R19 having their common connection connected to the inputs ofdriver circuit 36 and 38. Driver circuit 36 provides an output when theinput exceeds its threshold Vth. Driver circuit 38 provides an outputwhen the input drops below Vtl. In the absence of an input fromcontroller 1600 on the PWM2 line, the voltage at the node connecting R18and R19 will reach a mid-point between +V and ground and the resultantoutput of drivers 36 and 38 will keep both FET 42 and 52 off. As in thecase of the first phase, when the controller receives an internal enablesignal then the internal pulse modulated signal PWM is outputted to thedrivers and the respective high and low side FETs.

Refer now to FIG. 17, which illustrates an alternative technique forplacing the high side and low side FETs into a high impedance stateproviding the tri-state output. Elements corresponding to FIG. 16 havebeen assigned similar reference numerals and operate in a similarmanner. The difference from FIG. 16 is that the FIG. 17 embodimentprovides a dual pulse width modulated N drive control. Controller 1700includes logic elements 1702, 1704, 1706, 1708, 1710 and 1712 connectedas shown. A separate pulse width modulated signal (PWM) is sent to thehigh side FET of each phase. Driver 1720 includes driver circuits 1722and 1724 to drive phase 1 FETs 40 and 50. Driver 1730 includes drivercircuits 1732 and 1734 to drive phase 2 FETs 42 and 52.

Refer now to FIG. 18 which illustrates a dual PWM/enable technique forcontrolling the high side and low side FETs into a high impedance stateproviding the tri-state output. Controller 1800 includes logic elements1802, 1804, 1806, and 1808, connected as shown. Driver 1820 includesdriver circuit and logic elements 1822, 1824, 1826, 1828, and 1830connected, as shown. Driver 1830 includes driver circuit and logicelements 1922, 1924, 1926, 1928, and 1930, connected as shown. Theremaining elements are identical to those in FIG. 17 and are identifiedwith corresponding reference numerals. The FIG. 18 embodiment providesand enable signal when the high side FET and low side FET are intendedto operate in their normal PWM mode. In the absence of an enable signalboth the high side FET and low side FET are off, providing the desiredtri-state high impedance output.

Refer now to FIG. 19 which is a waveform diagram illustrating a 4 phaseexample of using a high impedance (tri-state) technique for transientcompensation. The four PWM waveforms are as shown in normal multi-phaseoperation. However, at the occurrence of a transient event the normalPWM1, PWM2, PWM3 and PWM4 pulses are suppressed and replaced with halfheight pulses. As a result, the Vout pulse has the desired lower outputwaveform with ATR, as compared with the excessive overshoot of an outputwaveform without ATR.

Refer now to FIG. 20, which is a schematic diagram showing the pulselimiting feature of the invention. The normal internal output of PWMgenerator 2000 is provided to gating circuit 2020. The ATRH1, ATRH2, andATRH3 signals are received in pulse limiting circuits 2010, 2012, and2014, respectively and combined in logic gate 2018. The ATRL signal isreceived on line 2008 into pulse limiting circuit 2016. The output oflogic gate 2018 and the output of PWM generator 2000 are combined inlogic gate and supplied to logic gate 2022 with the output of pulselimiting circuit 2016. The output of logic gate 2022 is the externaloutput of the pulse limited pulse width modulator.

In case of an ATRH or ATRL event, the ATR circuit detects an overvoltageor undervoltage condition during a transient event and responds byeither turning on all the low side FETs or turning on one or more of thehigh side FETs to compensate for the transient condition, minimizingovershoot and undershoot. By pulse limiting this overriding ATRcompensating signal (i.e. limiting the amount of time this circuit ison, then forcing it off for a fixed amount of time), the strength ofthis compensating action can be modified. This effectively changes thegain of this control mechanism. Varying the gain by adjusting the on andoff times allows the transient response of the system to be optimized.

Refer now to FIG. 21, which is a schematic diagram of a pulse limitingcircuit such as one of pulse limiting circuits 2010, 2012, 2014, or 2016in FIG. 20. The pulse limiting circuit includes programmable counters2100 and 2102, and logic gates 2104, 2106, and 2108 all connected asshown. Programmable counter receives a clock input signal. Asillustrated in the waveform diagram in FIG. 22, when the input pulsereceived at AND gate 2108 goes to its up level, the pulsed output goesto its up level because at that time TC1 (the output of programmablecounter 2100) is at its down level). As soon as TC1 goes to its uplevel, the pulsed output goes to its down level and remainscomplementary to the TC1 pulse until the input signal goes to its downlevel. The pulse limiting circuitry of FIG. 21 determines the duty cycleof the TC1 pulse.

What has then been described is a multi-phase pulse width modulatedvoltage regulator in which voltage excursions or deviations that exceedthe load line voltage by more than a pre-determined amount are detectedby an ATR circuit and a correction signal is applied. The correctionsignal is in the form of asynchronous pulses and the number of suchpulses is a function of the magnitude of the voltage excursion asdetermined by the number of thresholds that are exceeded. Transientresponse is further improved with an external ATR control circuit, atri-state mode of operation, AVP pre-positioning, as well as an adaptivefilter and pulse limiting techniques.

The present invention has been described above with reference to variousexemplary embodiments. However, those skilled in the art will recognizethat changes and modifications may be made to the exemplary embodimentswithout departing from the spirit and scope of the present invention.For example, the various components may be implemented in alternateways, such as, for example, by providing other configurations of SPC's.By way of another example, the number of phases utilized is a matter ofdesign choice. By way of a still further, the specific Pulse WidthModulator used to generate the PWM pulses is also a matter of designchoice. Such changes or modifications are intended to be included withinthe spirit and scope of the present invention.

The invention claimed is:
 1. A method of regulating voltage in amultiphase pulse-width modulated voltage regulator system comprising:providing an output current through a plurality of phases wherein only asingle phase is active at a time and at least one phase is inactive;setting multiple thresholds corresponding to deviations from apredetermined output voltage level in a second direction; comparing anoutput voltage to the thresholds; adjusting the output voltage accordingto the comparison of the output voltage to the thresholds by providing acompensation signal through at least one of the inactive phases, whereinthe compensation signal is generated according to the number ofthresholds that have been exceeded; detecting the current at an outputstage of the multiphase pulse-width modulated voltage regulator system;providing the detected current to a filter; and adjusting a bandwidth ofthe filter when detecting that one or more of the multiple thresholdshas been exceeded.
 2. A method of regulating voltage in a multiphasepulse-width modulated voltage regulator system as in claim 1, whereinthe predetermined voltage is along a load line.
 3. A method ofregulating voltage in a multiphase pulse-width modulated voltageregulator system as in claim 1, wherein the compensation signal isconfigured to activate a first inactive phase when a first threshold isexceeded.
 4. A method of regulating voltage in a multiphase pulse-widthmodulated voltage regulator system as in claim 3, wherein thecompensation signal is configured to activate the first inactive phaseand a second inactive phase when the first threshold is exceeded and asecond threshold is exceeded.
 5. A method of regulating voltage in amultiphase pulse-width modulated voltage regulator system as in claim 4,wherein the compensation signal is configured to generate a plurality ofcorrection pulses on inactive phases according to the number ofthresholds exceeded.
 6. A method of regulating voltage in a multiphasepulse-width modulated voltage regulator system as in claim 5, whereinthe plurality of correction pulses are asynchronous to a regularlyscheduled pulse-width modulator timing.
 7. A method of regulatingvoltage in a multiphase pulse-width modulated voltage regulator systemas in claim 1, wherein providing a compensation signal further comprisesblocking a synchronous pulse-width modulated pulse.
 8. A method ofregulating voltage in a multiphase pulse-width modulated voltageregulator system as in claim 1, further comprising: receivingpre-determined current values corresponding to the one or more of themultiple threshold values that have been exceeded; adding thepre-determined current values to the detected current at an outputstage; and providing a sum of the detected current and thepre-determined current values to the filter.
 9. A digital controller fora multiphase power regulator comprising: a multiphase pulse widthmodulator (PWM) configured to drive a plurality of phase signals whereinonly a single phase signal is active at a time and at least one phase isinactive during normal operation; an active transient response (ATR)circuit coupled the PWM, wherein the active transient response circuitis configured to: measure an output voltage; detect multiple thresholdlevels of deviations of the output voltage from the predeterminedvoltage level; and generate a compensation signal, wherein thecompensation signal drives the PWM to modify the phase signals accordingto the number of thresholds that have been exceeded; and an adaptivevoltage positioning (AVP) circuit comprising an adaptive bandwidthfilter configured to have selectable bandwidth comprising a narrowbandwidth and a wide bandwidth, and to be adjusted according to athreshold being exceeded.
 10. A digital controller for a multiphasepower regulator as in claim 9, wherein the predetermined voltage isalong a load line.
 11. A digital controller for a multiphase powerregulator as in claim 9, wherein the compensation signal is configuredto drive the PWM to activate a first inactive phase according to adeviation of a first threshold.
 12. A digital controller for amultiphase power regulator as in claim 11, wherein the compensationsignal is configured to drive the PWM to activate the first inactivephase and a second inactive phase according to a deviation of a secondthreshold.
 13. A digital controller for a multiphase power regulator asin claim 11, wherein the PWM is configured to activate the first phaseasynchronously relative to a regularly scheduled PWM timing.
 14. Adigital controller for a multiphase power regulator as in claim 9,wherein the PWM is configured to modify the phase signals by providing aplurality of correction pulses on a first inactive phase.
 15. A digitalcontroller for a multiphase power regulator as in claim 9, wherein thecompensation signal is further configured to block a PWM pulse.
 16. Adigital controller for a multiphase power regulator comprising: amultiphase pulse width modulator (PWM) driving a plurality of phasesignals wherein only a single phase signal is active at a time and atleast one phase is inactive during normal operation; an active transientresponse (ATR) circuit coupled the PWM, wherein the active transientresponse circuit is configured to: measure an output voltage; detectmultiple threshold levels of deviations of the output voltage from thepredetermined voltage level; generate a compensation signal, wherein thecompensation signal drives the PW to modify the phase signals accordingto the number of thresholds that have been exceeded; and an adaptivevoltage positioning (AVP) circuit comprising: an adaptive bandwidthfilter configured to have selectable bandwidth comprising a narrowbandwidth and a wide bandwidth; and a summing circuit configured toreceive pre-determined current values corresponding to the one or moreof the multiple threshold values that have been exceeded, add thepre-determined current values to a detected current at a power stage andprovide a sum of the detected current and the pre-determined currentvalues to the adaptive bandwidth filter.